1. Field of the Invention
This invention relates to methods of and apparatus for spatially interpolating between lines of a digital video signal to produce interpolated lines.
2. Description of the Prior Art
Requirements exist for converting an interlace scanned video signal into a progressively scanned (sometimes called sequentially scanned) video signal. This involves converting interlace scanned fields of a video signal, each of which comprises the odd or even scan lines only of a frame of the video signal, into progressively scanned fields each comprising a full set of both odd and even scan lines. Examples of where such a requirement arises are where a picture is to be displayed in slow motion, and where it is required to improve the performance of a video display monitor.
One previously proposed method employs a simple technique of vertical (spatial) interpolation (filtering) to produce an interpolated (progressively scanned) field from a single input field. Another previously proposed method involves a motion adaptive technique in which a vertical filter (interpolator) is used for moving picture areas and a temporal filter (interpolator)--which interpolates between input fields--is used for static picture areas. The motion adaptive technique is advantageous over the purely vertical interpolation technique in that, in static areas, the picture represented by the progressively scanned field has full vertical resolution. However, the vertical resolution is visibly reduced in moving areas.
It is an object of the invention to provide a method of interpolation in which the degradation of vertical resolution can be reduced.
Another object of the invention is to provide an interpolation apparatus in which the degradation of vertical resolution can be reduced.